1. Field of the Invention
The present invention relates to a radio link protocol, and more particularly to a method for inserting a Length Indicator (LI) in a Radio Link Control (RLC) that selectively controls LI value insertion so that any LI to be inserted in the next PDU may be prevented from being unnecessarily included.
2. Background of the Related Art
The current trend in communications technology is concentrating research into allowing access of multimedia applications without restrictions on time/space and endeavors for visible achievement thereof. The development of digital data processing and transmission technology is consequently on the verge of realizing a real time global data communication system via satellites in which wire and radio communications are unified.
Also, the development of digital data processing and transmission technology allows still and dynamic images to be transmitted in real time via a network, as well as allowing the previous voice communication and information to be accessed freely without discriminating between wire and radio communication at any time and place. International Mobile Telecommunication-2000 (IMT-2000) will be an example thereof.
The Radio Link Control (RLC) layer presented in the invention is the second layer of 3 GPP, which has two kinds of Packet Data Units (PDUs). They are an Unacknowledged Mode Packet Data Unit (UMD PDU), used when the acknowledgment signal transmission to a sending side is not necessary after receiving the PDU in a receiving side, and an Acknowledged Mode PDU(AMD PDU). Each PDU format is as shown in FIG. 1 and FIG. 2, respectively.
As shown in FIG. 1, a format of the UMD PDU is composed of a header, a LI group, data, and a PAD (Padding). The header is composed of a 7 bit Sequence Number as a field for indicating the sequence number of each PDU, and a 1 bit Extension (E) field to indicate if the next field is data or LI and E bit. The data group is a field corresponding to the Service Data Units (SDUs) descended from an upper layer including at least one SDU. Since such a data group is variable in magnitude, a padding is carried out for octet aligning the overall PDU size.
Here, the PDU is sourced from ITU-TX.200/ISO-IEC7498-1, and the SDU is sourced from ITU-TX.140.
As shown in FIG. 2, a format of the AMD PDU includes a header, a LI group, and data. In the AMD PDU, a piggyback type status PDU is inserted instead of the padding to enable the transmission.
The header of the AMD PDU additionally has a 1 bit D/C field to indicate if the pertinent PDU is loaded with data information or control information, a P field as a 1 bit polling field for requesting a status report to the receiving side, and a 2 bit Header Extension (HE) field for notifying if the next data is data or LI and E bit.
In the above UMD PDU and the AMD PDU, the LI group is composed of the LI and E bit, in which each of the LIs is a field for indicating the boundary of each SDU when the PDU includes several SDUs. Each LI indicates the number of octects from the first octet in the data group to the last octet of each SUD. The LI group means the LIs for the SDUs included in one PDU. The LI size is 7 bits or 15 bits.
In the case of the AMD PDU, the 7 bit LI is used if the PDU size is at most 126 octets, and alternatively, the 15 bit LI is used. In the case of the UMD PDU, the 7 bit LI is used if the PDU size is at most 125 octets, and alternatively, the 15 bit LI is used.
Some values of these LIs are predefined for use in specific purposes.
Table 1 illustrates LI values for a specific purpose (In the case of the 7 bit LI), and Table 2 illustrates LI values for a specific purpose in the case of the 15 bit LI.
As can be seen from FIG. 1 and FIG. 2, if the end of one SDU (referred to as A) correctly matches the end of the PDU, the first LI value of the very next PDU (referred to as B) is inserted as ‘LI=0’ to so indicate.
In the case of the 15 bit long LI, if the last segment of the RLC SDU is one octet insufficient to the end of the PDU, the first LI of the very next PDU has the value of ‘111 1111 1111 1011’ to so indicate. Also, the PDU uses ‘LI=1’ as a value to indicate that the rest part of the RLC PDU is a padding, where the padding is necessarily positioned at the last of the RLC PDU.
TABLE 1Length: 7bitBitDescription0000000The previous RLC PDU was exactly filled with the lastsegment of an RLC SDU.1111100Reserved1111101Reserved1111110AM PDU: The rest of the RLC PDU includes a piggy-backed STATUS PDU. UM PDU: Reserved1111111The rest of the RLC PDU is padding.
TABLE 2Length: 15bitBitDescription000000000000000The previous RLC PDU was exactly filled with thelast segment of an RLC SDU.111111111111011The last segment of an RLC SDU was one octetshort of exactly filling the last RLC PDU.111111111111100Reserved.111111111111101Reserved.111111111111110AM PDU: The rest of the RLC PDU includes apiggybacked STATUS PDU. UM PDU: Reserved.111111111111111The rest of the PDU is padding.
FIG. 3 illustrates the ends of the SDUs in one PDU by using the 7 bit LI in the AMD PDU. Here, the PDU size is 35 octets and the data size included in the PDU is 24 octets.
As can bee seen in FIG. 3, the AMD PDU has three SDUs, for example SDU1, SDU2, and SDU3. Each of the SDUs has the size of 11 octets, 9 octets and 4 octets, respectively. The LI values for accumulatively indicating the octet numbers from the first octet to the last octet of each data part of SDU1, SDU2, and SDU3 are inserted as 11 (octet), 20 (octet) and 24 (octet), and more inserted with ‘LI=111 1111’ to express the rest part of the PDU is a padding (5 octet).
In the related art, LI=‘0’ is inserted into the very next PDU (B) in all the cases where the end of one SDU (A) exactly matches the end of the PDU in the RLC PDU.
FIG. 4, FIG. 5, and FIG. 6 illustrate three cases where LI=‘0’ is inserted according to a method for inserting LI of the related art, in which FIG. 4 shows a proper process, while FIG. 5 and FIG. 6 show problems of unnecessary LI value insertions.
Referring first to FIG. 4, LI=‘0’ is attached to the next PDU. If the LI for the SDU2 in FIG. 4 is included in the current PDU, one octet data of the SDU2 is necessarily shifted to the next PDU due to size of the LI. In other words, if a cumulative sum of LI=22 is recorded in the octet under LI=12 to indicate the end of SDU2, since the currently set PDU size is 25 octets and the sum octet of components of the PDU is 25, the sum octet of the PDU components becomes 26 and the end of the SDU2 does not match the end of the pertinent PDU. Then, it is meaningless to attach the second LI (LI=22).
Therefore in this case, LI=‘0’ is inserted into the first LI of the next PDU (B) instead of inserting the second LI in the first PDU (A) to indicate the end of the SDU2.
However, in the cases as illustrated in FIG. 5 and FIG. 6, the pertinent PDU (A) itself shows that the last SDU of the PDU (A) fits exactly into the PDU (A), including the various LIS, so that LI=‘0’ need not be attached to the next PDU(B). Accordingly, the related art has various problems.
For example, the LI=‘0’ value indicating that the last segment of the very previous SDU exactly matches the end of the previous PDU is unnecessarily inserted to the very next PDU (B) even though the LI indicates the end of the SDU2 of the PDU(A) as shown in FIG. 5.
Also, the LI value or the LI=‘0’ value is inserted to notify that the end of the pertinent PDU (A) (the middle PDU in FIG. 6) is the padding since the end has one excessive octet (causing ‘0’ padding as the position of the padding disappears due to the insertion of the final LI) as shown in FIG. 6. Thus, inserting the LI=‘0’ value in the very next PDU (B) is unnecessary since the LI=‘1’ value means that the end of the pertinent PDU (A) correctly matches the last segment of the SDU2.
In the dotted part under the SDU 2 of the pertinent PDU(A) of FIG. 6, the PDU(A) size is 27 while the sum of the components of the PDU is 26 leaving 1 octet. Therefore, the remaining one octet is padded as LI=1111111.
The aforementioned problems are observed also in the UMD PDU as same as in the AMD PDU. Therefore, according to the method for inserting LI of the related art, the LI value or LI=‘0’ value is unnecessarily inserted into the LI group of the PDU, which includes unnecessarily overlapped information thereby wasting network sources.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.